The present invention relates to combustion turbines and more particularly to systems for limiting the energy input to the turbine for safety and product protection purposes.
The fuel flow to a combustion turbine can vary rapidly as the turbine is being controlled to satisfy startup or load requirements. In turn, large and rapid fuel flow variations can have a large effect on temperature variation of the turbine blades and other engine parts. It is desirable to limit fuel flow to limit turbine temperature swings and thereby reduce cyclic thermal stress damage to the turbine, especially during acceleration to synchronous speed.
Thermocouples have been employed to monitor turbine temperature with limit control action being taken when required. However limit action based on thermocouple temperature detection is based on temperature increases which would already have occurred and which accordingly already have shocked the turbine. Further, thermocouple devices must have sufficient mass to be durable and reliable in the turbine environment, and the time constant associated with such mass places a delay on any potential limit action. It has also often been the practice only to monitor fuel pressure or flow during the 10 to 15 second ignition period to detect a possible catastrophic throttle valve failure after ignition and successful valve operation.